Charles Darwin was plagued by a mysterious chronic disease. It had a variety of symptoms including nausea, fatigue, and neurological problems that sometimes incapacitated him for weeks. His voyage on the Beagle is even more remarkable considering the misery of his "seasickness" during the trip. Based on his symptoms and those of family members, it is thought that Darwin may have suffered from a defect in mitochondrial DNA. What is the likely consequence of such a defect?